1. Field of the Invention
This invention generally relates to an optical disc recording/reproducing system, and, in particular, to a tracking control system of an optical pick-up for use in such an optical disc recording/reproducing system.
2. Description of the Prior Art
As an auxiliary storage device of a computer system, use has been widely made of a magnetic recording medium, such as magnetic tape and magnetic disc. Recently, it has been proposed to utilize an optical recording medium as an auxiliary storage device of a computer system so as to obtain an increased recording density.
For example, in an optical disc, in which an optical recording medium is formed in the shape of a disc, data is recorded by forming pits or small recesses of the order of 1 micron in diameter at a pitch or spacing of the order of 2 microns on a recording track on the surface of the disc by the application of a laser spot. The recording capacity is on the order of 10.sup.11 to 10.sup.12 bits for a disc of approximately 30 cm in diameter. Since an optical disc has such a large recording capacity, it is also proposed to use as an image file system for storing image information which is usually extremely large in the amount of information to be recorded.
Typically, a recording track is defined on a disc in the form of a pre-groove at the time of its manufacture, and the recording track or pre-groove is previously provided with various information, such as identification information of a recording region and sync signal, so as to properly control data to be stored. In one form of an optical disc, a plurality of such recording tracks are provided concentrically; whereas, in the other form, a single recording track is provided on an optical disc spirally.
In order to write and read data to and from an optical disc, provision is typically made of an optical pick-up which is movable radially with respect to the optical disc. Such an optical pick-up typically emits a laser beam toward the optical disc, and the reflected laser beam is received by the optical pick-up, whereby the received laser beam is analyzed to extract information recorded on the optical disc in the form of a series of pits. On the other hand, the laser beam applied to the optical disc from the optical pick-up may be modulated in accordance with information to be recorded, so that desired information may be recorded on the optical disc in the form of a series of pits. It is to be noted that such an optical pick-up is required to be properly aligned with a recording track for writing data thereon or reading data therefrom at the accuracy on the order of .+-.0.1 microns. For this purpose, there must be provided a tracking control system for allowing the optical pick-up to be properly aligned with a recording track of the optical disc.